This application claims the priority of German Patent Document 198 36 017.7 filed Aug. 10, 1998 and PCT/EP99/05834 filed Aug. 10, 1999, the disclosures of which are expressly incorporated by reference herein.
The invention concerns a procedure for allocating braking power at wheels of the front and rear axles on a vehicle coming to a stop by way of self-acting brake intervention.
On vehicles equipped with service brakes, which enable a self-acting brake intervention, several different safety and comfort functions can be realized. Such braking systems for instance, are powered electromechanically, or electrohydraulically and are preferably constructed as brake-by-wire-systems. This way, for example, a vehicle may be stopped by activation of the wheel brakes by the braking system without intervention of the driver. In order to achieve a sufficient stopping effect at the lowest possible energy deployment (i.e. for the electric engines at the wheel brakes, or for the hydraulic pump), the wheel brakes both at the front and rear axles will be activated.
If at the same time a steering maneuver on a vehicle parked in this way is being performed, an increased power demand is created for the steering motions, as would be the case with stationary, non-braked front wheels. This increased power demand must be exerted by way of an appropriate energy supply for a power-assisted or power activated steering system. Additionally, the steering system must be proportionally sized to the maximum amount of this type of steering power.
It is the object of the invention to provide a procedure which reduces the energy demand for the steering maneuver on a parked vehicle.
The main objective is to reduce the braking power on wheels of the front axle during steering motions on a fully stopped vehicle. This leads to benefits with regard to the energy demand during steering maneuvers, for instance during parking procedures. With the procedure according to the invention, a reduction of the steering power is achieved on a stationary vehicle, with the condition of the design of a power-assisted, or power activated system, which produces an increased steering power, already being critical. Therefore, the steering system can be designed proportionately weaker with beneficial results in energy absorption, weight, size, manufacturing costs, etc. The reduction in steering power is especially important in electronic power-assisted and purely power activated systems, as for instance in steer-by-wire-systems.
An intervention on the braking system of a vehicle, which depends on a steering maneuver, is generally known in the form of so-called steering brake systems for agricultural towers or such, as shown, for example, in EP 0 275 985 A, or EP 0 314 641 A. However these well known systems differ significantly from the present invention.
The procedure according to the invention may be used in all xe2x80x9cactive braking systemsxe2x80x9d that involve actuators, which can be controlled by the driver without engaging the pedals.
The reduction of the stopping power on the front axle in accordance with the invention can lead to an insufficient stopping effect on a vehicle parked on an inclined surface. Therefore it is advantageous to compensate the loss of braking power on the front axle with a simultaneous increase of the braking power on the rear axle of the vehicle, if necessary, in order to ensure a sufficient stopping effect for the vehicle as a whole.
The reduction of braking power on the front axle takes place as a function of the steering angle of the front wheels. The function between steering angle and braking power can generally be defined as desired. Depending on the steering angle, the appropriately associated steering momentum is thereby achieved. For instance, the applied braking power can be reduced on the front axle continually with an increasing steering angle, in order to continue to ease the steering procedure with sharply turned front wheels.
Additionally, it is possible to change the braking distribution depending on the changing speed of the steering angle dxcex1/dt, if necessary.
The inclination of the vehicle is taken into consideration with the braking distribution in order to prevent the vehicle from rolling away, in any event. Additionally, the mass of the vehicle (load, trailer operation, etc.) can be considered with the rating of the braking power. Of course, other influencing factors may be used for the rating of the braking power, as, for instance, the temperature of the braking components, vehicle-specific special features of individual models of one vehicle make, or the measure of the desired steering power assistance.
In order to increase the braking power on the rear axle in addition to the increased stopping effect on the rear axle of the vehicle it is possible to use a stopping brake system, which is usually activated only when exiting the vehicle (for instance by electromotive force). This helps to apply an increased amount of braking force on the rear axle, in order to further reduce the braking power on the front axle and therefore further reduce the steering power. A known parking brake system is exemplified by EP 0 456 097 A or EP 0 595 570.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.